Assessment of penetration depth and toxicity of titanium dioxide nanoparticles in barrier-defective skin after UV exposition

二氧化钛纳米粒子在紫外光照射下的光催化活性会导致遗传有害的活性氧物种(ROS)的形成。二氧化钛纳米颗粒用于化妆品和防晒霜。虽然它们不会穿透健康皮肤的皮肤屏障，但它们可能能够穿透表皮的最外层(角质层)，进入患有疾病的皮肤的活跃层，这些疾病限制了其自然屏障的功能。有理由担心，即使是少量的光催化活性颗粒到达活组织，也会导致侵略性ROS的形成，特别是在紫外线照射下。然后，这些物质会破坏皮肤深层的细胞和遗传物质，从而增加患皮肤癌的风险。虽然广泛的研究表明，含有纳米二氧化钛颗粒的防晒霜可以安全地应用于健康、未受损的皮肤，但对于疾病受损的皮肤或因晒伤、风、咸水或沙子而受到压力的皮肤，防晒霜的安全使用仍不清楚。因此，这个项目的目的是帮助评估含有二氧化钛纳米颗粒的防晒霜和化妆品对屏障受损皮肤患者的风险。在联合的初步工作中，申请者成功地测试了全反射X射线荧光光谱(TXRF)，作为一种适合于检测皮肤标本切片中钛的方法。结合使用XRF方法和拉曼显微镜，可以追踪二氧化钛纳米颗粒在受损皮肤中的扩散轮廓。研究还证明，用防晒霜处理的冷冻皮肤样品可以用聚焦离子束切割，然后在冷冻扫描电子显微镜中进行分析。拟议的项目将从分析覆盖有二氧化钛纳米颗粒的紫外线照射细胞培养物中的光催化反应开始。在小鼠模型中，以人类皮肤样本为例，测定紫外线照射后二氧化钛纳米颗粒在屏障干扰皮肤中的渗透深度，并与健康皮肤进行比较，这构成了研究的核心。此外，还将研究二氧化钛纳米颗粒对表皮分化、增殖、稳定性和完整性的影响，并将识别和表征DNA损伤。关于二氧化钛纳米颗粒在屏障障碍皮肤中的渗透深度和毒性的新发现，将为改进含有二氧化钛的化妆品，特别是防晒霜，治疗皮肤屏障障碍患者的风险评估做出重要贡献。

The photocatalytic activity of titanium dioxide nanoparticles under UV irradiation in the presence of water leads to the formation of genetically harmful reactive oxygen species (ROS). Titanium dioxide nanoparticles are used in cosmetics and sunscreens. While they do not penetrate the skin barrier in healthy skin, they may be able to penetrate the outermost layer of the epidermis (stratum corneum) and enter living layers of the skin suffering from diseases which limit its natural barrier function. There is reason to fear that even small amounts of photocatalytically active particles reaching living tissue, lead to the formation of aggressive ROS, especially under UV irradiation. These can then damage the cells and the genetic material in the deeper layers of the skin and thus increase the risk of skin cancer. While extensive studies have shown that sunscreens containing nanoscale titanium dioxide particles can be safely applied to healthy, undamaged skin, the safe use of sunscreens on disease-damaged skin or skin stressed by sunburn, wind, salt water or sand is still unclear. Therefore the aim of this project is to contribute to the assessment of the risk posed by sunscreens and cosmetic products containing titanium dioxide nanoparticles to patients with barrier-damaged skin.In joint preliminary work, the applicants have succeeded in testing total reflection X-ray fluorescence spectroscopy (TXRF) as a suitable method for detecting titanium in microtome sections of skin samples. Using a combination of XRF methods and Raman microscopy, it is possible to trace diffusion profiles of titanium dioxide nanoparticles in damaged skin. It has also been demonstrated that frozen skin samples treated with sunscreens can be cut with a focused ion beam and subsequently analyzed in a cryo-scanning electron microscope.The proposed project will start with the analysis of the photocatalytic reactions in UV-irradiated cell cultures covered with titanium dioxide nanoparticles. The determination of the penetration depth of titanium dioxide nanoparticles in barrier-disturbed skin after UV irradiation in comparison to healthy skin in a mouse model and using human skin samples as an example, forms the core of the investigations. Furthermore, the influence of titanium dioxide nanoparticles on epidermal differentiation, proliferation, stability and integrity will be investigated and DNA lesions will be identified and characterized. The new findings on the penetration depth and toxicity of titanium dioxide nanoparticles in barrier-disturbed skin will make an important contribution to improved risk assessment for the use of cosmetics containing titanium dioxide, especially sunscreens, for patients with skin barrier disorders.